BANGOR, Maine — Bangor Public Library’s head of maintenance feels like he’s using his fingers to plug leaks in a dike.

“I’ve run out of fingers,” Terry Balden said Friday, standing on the roof that has caused him headaches during the past year.

The Bangor library’s iconic, oxidized copper roof and dome are original to the building, which opened in 1913, about two years after a devastating fire left much of Bangor in ruins. The “Great Fire of 1911” took the majority of the original library’s 70,000-book collection with it.

A century after its trial by fire, the library and its more than 500,000 volumes face another threat — water.

The building’s 100-year-old copper roof is beyond repair and must be replaced, according to architects and engineers who have assessed the damage. That replacement is projected to cost about $3 million.

The library’s entire budget in 2012 was $2.25 million. To reach the $3 million figure, library officials are in the planning stages of an enormous fundraising effort.

“Our most precious resource — our collection — is in imminent danger from the leaks, and failure to address the realities of the situation could compromise further the integrity of the building,” according to library campaign materials.

In the second-floor Bangor Room, which houses volumes that chronicle the city’s early years, as well as genealogical records, the roof has failed, causing the ceiling to drop nearly three inches. The library put up scaffolding in October to brace the ceiling and prevent a potential collapse.

During a heavy rainstorm in October, library employees entered the building to find a “waterfall” coming down the marble staircases at the main entrance, McDade said.

The dome is leaking, allowing water to seep inside and threaten the intricate plaster of Paris work inside. Pigeons also have taken up roost inside the dome, leaving droppings as evidence. A blue tarp and a piece of plywood have served as temporary fixes.

Problems aren’t limited to the 100-year-old roof. In a portion of the library’s 1950s-era expansion, a tarp covers two stacks to protect a section of older fiction books from a leak.

“There’s a complex bucket system,” McDade joked. An assortment of plastic buckets sit on the water-stained carpet. One bucket hangs from a pipe in the ceiling to catch water from the leak above. The library managed to save those water-damaged books after drying them out and checking for mold.

While there have been problems with the roof in the past, this fall and winter have been the worst by far, McDade said. Most of the problems are caused by “pitted” sections of copper, where the weight of snow and ice have caused depressions and weakened the metal.

The library tried to stem past problems by using rubber to patch failing areas of the roof, but now that extensive patchwork is beginning to falter.

“We’ve mended as much as we can,” McDade said.

Both the original roof and the roof in the section built in the 1950s have outlived their useful lives, according to the library’s consultant on the roof project, Robert Fulmer, who has more than 30 years experience in design and repair of copper and slate roof systems. Repairs aren’t required for the roof of the 1997 addition to the library.

In a recent memo, Fulmer told McDade and the library board of trustees that copper typically has an 85-year service life. The 1950s roof was expected to last 20 years.

Fulmer said another copper roof was the only replacement material that had the essential characteristics that the library needs — malleability, durability, longevity and historic aesthetics. A new copper roof would last another 80 to 100 years, officials have said.

Bangor Public Library is soliciting bids from contractors for the work. Those bids are due this month, according to the library. Balden said at least six potential bidders have examined the roof, including some who clambered over it Friday morning. McDade said the old copper roof would be sold for scrap, mitigating the cost of the new roof.

McDade said the library hopes to begin construction in June, if the funding is available.

The original library was founded in 1830 as the Bangor Mechanic Association’s private library. The library was opened to the public in 1883 thanks to a $100,000 bequest from lumber baron and former U.S. Rep. Samuel F. Hersey.

“What is under this roof is a treasure,” one that needs to be protected, said Kate Villa, campaign director for the library.

As Bangor Public Library, which had 243,000 visitors in 2012, kicks off its substantial fundraising effort, it also is eyeing other potential renovations to modernize the facility’s interior, Villa said.

As technology evolves, the design of libraries is changing, Villa said.

Officials are looking for feedback from the public on what they’d like to see in the library. A survey is available at www.surveymonkey.com/s/PCVVWQM. Participants will receive a $3 coupon from Governor’s Restaurant.

The library will host a series of focus groups in late March to seek feedback from the community on what they want the library to look like in the future. The first is scheduled 5-6 p.m. March 18 at the library. The second will be held two days later at the same time.

Those interested in participating should contact Villa at kvilla@bpl.lib.me.us or 947-8336, ext. 105.